Commercially today, many monomeric materials, and particularly vinyl chloride, are being polymerized on a large scale either in aqueous suspension or in aqueous dispersion, i.e., latex foam, employing colloidal suspension agents or soaps and/or synthetic detergent-type dispersing agents. In these methods of polymerization, moderate to vigorous agitation is depended on to suspend and/or disperse, and to maintain such suspension or dispersion, during polymerization and to assist heat transfer to reactor cooling surfaces. However, polymer particles produced in accordance with these processes are not uniform in size and shape. In processing such polymers as, for example, polyvinyl chloride (PVC), it is desirable, and very often necessary, to have uniform size and shape in the polymer particles.
Various methods and modifications of existing processes have been proposed to obtain uniform polymer particle size. For example, one very successful method proposed is that described in U.S. Pat. No. 3,620,988. In this process a monomeric material, such as vinyl chloride, of low solubility in water containing a monomer-soluble free radical type catalyst, is suspended as discrete droplets of a desired size in an aqueous medium thickened with a water-insoluble highly gelled polymeric suspending or dispersing agent which imparts plastic flow properties to such medium. The polymerization reaction is then carried out using a batch or continuous process under substantially quiescent conditions, that is, in the absence of turbulence or the absence of shearing forces sufficient to deform the suspended droplets or monomer and/or to damage the polymer bead at any stage of conversion. When polymerizing vinyl chloride by such a process, the uniform beads of PVC that are formed are normally clear and glassy in nature.
There are many cases where porous polymer beads are desirable, such as where the polymer, such as PVC, is to be employed in extrusion operations. Porous beads would also be desirable in the case of PVC where, because of Government regulations, it is necessary to remove substantially all the unreacted vinyl chloride therefrom. A porous polymer bead would greatly facilitate such removal.